Process of manufacturing and finishing coated paper, and resultant product



Deci 7, 1965 M. M BRUNDIGE ETAL 3,222,209

PROCESS OF MANUFACTURING AND FINISHING COATED PAPER, AND RESULTANT PRODUCT Filed June 8, 1964 N .@E NDMW l: mm g O n mw G Umn wm mm mwwflmm mm mm m 5 E E 8 O Q 0 a a 8 O R NJ 0 i m M T H N m0 w WD N AE SF IN W W 3" w 0 NJ MD l mm RD U A M B N. E -Nam United States Patent PROCESSOF MANUFACTURING AND FINISHING COATED PAPER, AND RESULTANT PRODUCT Maurice M. Brundige, Westernport, and David N. Obenshain, Luke, Md, John H. Fredrickson, Keyscr, W. Va.,

and Harry F. Kohne, Jr., Blooiniugton, Md., assignors This application is a continuation-impart of application Serial No. 80,646, filed January 4, 1961, now abandoned.

This invention relates to an improved process and apparatus for manufacturing and finishing coated paper, and to the resultant product. More particularly, it relates to a coating andfinishing operation performed on-the-machine to produce high grade coated papers which exhibit the qualitiesiof good printing smoothness and freedom of mottle as a result of a unique double coating and finishing process.

In general, most methods employed in coating operations on paper and paperboard may be classed as either roll coating or doctor coating. In the former operation, a layer of coating material is deposited upon a traveling web of paper by being transferred froma coating applicator roll in contact with the web. It is very difiicult to produce a smoothly coated web in this fashion due to the formation of a pattern on the surface caused by film splitting at the exit nip, such pattern often being referred to as a nip pattern or roll pattern, which is seemingly an inherent characteristic of roll coating.

It has long been known in the art that coating may be applied to paper through the action of some type of doctoring or trowelling device. serving to meter and smooth the coating onto a traveling web of paper. Such devices usually take the form of doctor rods or doctor blades, but, regardless of the form, their function is generally the same, to meter and smooth coatings on the traveling web.

In certain instances, it is desirable to double coat a traveling web of paper, that is, to apply a second layer of a coating material over a first layer of the same or different coating composition. The objective of such an operation may be the utilization of a relatively inexpensive base coating, employing a premium coating only in the top coat. Another object may be the manufacture of, coated paper possessing high coat weights for the purpose of enhancing brightness, opacity, printability, and smoothness.

It has been found that a, web of coated paper with an extremely smooth surface can be produced through the use of two doctor blades in the application of two layers of coating material on each side of a traveling web of paper.

A first layer of coating is smoothed onto theweb and excess coating is wiped off the web by a doctor blade. A second layer of coating is applied to the surface of the first coating layer, and a second doctor blade serves to wipe excess coating from the web and to smooth the surface of the second coating layer. The first coating layer tends to fill in the low areas of the basestock by being trowelled into those areas by the doctor blade and produces a relatively smooth surface, over which the second layer of coating is applied and again smoothed by the action of a doctor blade to produce a surface of uniformity and smoothness heretofore unknown in the art of double coating.

It has been found that the final smoothness of the coated sheet greatly depends upon the smoothness, of the first coating layer. Application of this layer of coating by roll coating produces a surface of non-uniform smoothness due to the roll pattern formed. A second layer of coating applied by docotor blade merely tends to fill in the 3,222,209 Patented Dec. 7, 1965 low areas of the roll pattern and the ultimate printing smoothness is inferior to awe]: of paper double coated by two doctor blade coaters. The final printing quality of paper that is coated by a roll coater followed by a blade ooater is also inferior to paper that is double coated by two blade coaters according to the present invention.

Paper coated by the process of double doctor blade coating could be finished in the conventional manner of supercalendering the coated web in an oifmachine process. A supercalender stack is made up of hard surfaced metal rolls alternated with resilient non-metal rolls such as compressed paper or cotton rolls. Paper is passed through the nips formed by the supercalender rolls, and the web is pressed against the metal rolls by the resilient rolls.

Pressures at the bottom nip are usually in the. range of,

1200 to 1600 pounds per linear inch of nip. Paper finished in this manner has a very glossy surface, with good printing smoothness and substantial freedom of mottle. The word mottle as used in this specification and claims is intended to cover the non-uniformity of gloss that coated papers frequently exhibit when finished in particular finishing operations, as will be disclosed hereinafter. Because of the excellent quality of coated paper finished by the action of a supercalender, this finishing method is used. extensively in the art of manufacturing high grade coated papers.

Ooatedpaper has also been finished on the paper machine by the action of on-the-machine calender stacks. A machine calender stack consists of hard surfaced metal rolls, such as chilled iron rolls, which are loaded to pressures very substantially less than the pressure loadings to which supercalender rolls are subjected. Paper is passed through the machine calender stack in a continuous web, while the web is still on the paper machine. With coated papers, a high degree of surface smoothness can be obtained due to the flattening action of the calender rolls, but the coated paper will also possess objectionable non-uniformity of gloss. The metal rolls are too hard to yield and conform to the surface of the web being calendered, and high spots in the web are densified and polished more than low spots immediately adjacent thereto, The polishing of these high spots creates a differential in the gloss between the high areas and low areas of the web, and thus contributes to a non-uniform surface gloss defined as mottle. Mottle is objectionable in high grade printing papers because it detracts greatly from the overall uniforni appearance of the paper upon subsequent printing. Nonuniform densification of paper affects the ink absorptivity of the paper, which also contributes to a non-uniform surface gloss after printing.

It has been greatly desired to produce paper having the qualities of good printing smoothness and freedom of mottle in one continuous operation, such as by the finishing of a coated web of paper while it is still on the paper machine. Because the final finishing operation heretofore could not be accomplished by chilled iron rolls in a machine calender stack due to the mottle developed on the surface of the coated Web, a resilient roll. has long been sought which could be placed in a machine calender stack and withstand the operating conditions to which a roll in a machine calender stack is subjected, and at the same time the roll would yield to conformto the surface of the paper web and polish it in a uniform manner. While cotton rolls have the ability to uniformly finish coated paper, as is seen by their action in a supercalender stack, they are not damage resistant enough to withstand the battering that rolls in a machine calender undergo during web threading operations or other situations such aswrap-ups of paper around the calender rolls and web breaks. During a web break, the tail of the web passing through the stack becomes creased and folded over, and

concentrates the load on the stack in a few areas while leaving immediately adjacent areas with substantially no load. This high pressure is sufficient to permanently deform a cotton or paper filled roll. The deformations caused in the surfaces of these rolls prevent uniform finishing of a coated paper web.

Finishing paper in a single on-the-machine operation eliminates the added step of supercalendering. Paper coming off apaper machine must be transported to the supercalender for further finishing, and there usually is an added step of rewinding the paper before it is supercalendered. The time involved in handling the paper in separate operations, as well as the capital investment and maintenancecosts, makes a continuous manufacturing and finishing operation on-the-machine very desirable.

It ha been found that the qualities of good printing smoothness and freedom of mottle can be afforded a coated web of paper by coating the web by double doctor blade coating and by finishing the coated web by the action of certain resilient rolls at calender pressures up to 600 pounds per linear inch, all while the web is on a paper machine, thus eliminating the separate off-machine supercalendering operation while maintaining the benefits of such an operation. The resilient rolls employed in this fashion in a machine calender stack may also be used in a supercalender in place of cotton rolls to finish paper.

We have found that resilient elastic composition rolls, having a hardness within certain specified ranges and possessing the ability to resist the normal battering encountered by rolls in a machine calender stack, can be used in a machine calender or supercalender stack to finish paper. The term elastic composition roll used throughout the specification and claims may be defined as a roll comprising a metal inner mandrel and an outer cover of an elastic composition or plastic material. The first requisite of such a roll for use as a calender roll is that it be hard enough to develop gloss and smoothness on a coated web of paper when used in a calender stack. It has been found that such rolls can be provided, having the necessary hardnesses, possessing sufficient elasticities, even greater than cotton rolls, which are able to conform to the paper being calendered on-the-machine, and which can develop uniform gloss and good printing smoothness with freedom of mottle. These rolls also possess considerably more ability than cotton or paper rolls to recover from the deformations that are encountered in the battering to which rolls in a machine calender are subjected. Finally, these rolls have the ability to maintain suitable hardnesses up to temperatures which exceed those conditions normally encountered on a machine calender or supercalender stack.

The invention will be best understood by reference to the following detailed description and drawing forming part of this specification in which:

FIGURE 1 is a diagrammatic representation of the process and apparatus employed in the present invention;

FIGURE 2 is an elevational view of an elastic composition roll forming part of the invention; 4 FIGURE 3 is an enlarged and exaggerated illustration of the cross section of a sheet of paper which has been double coated according to the present invention.

Referring to FIGURE 1 of the drawing, a traveling web of paper P is passed through the first blade coater comprising a backing roll and an applicator roll 11, both rolls rotating in the direction of web travel. Applicator roll 11 rotatively carries coating 12 from the coating pan 13, and applies coating to the web P on the side of web P referred to as the wire side. Doctor blade 14 (shown in a trailing position in relation to web travel and referred to as a trailing blade) serves to act upon the coated web to smooth the coating and to limit the amount of coating which passes the doctor blade 14 to a predetermined thickness. Coating is trowelled into the low areas of the basestock (web P) and the resultant coated web has a relatively smooth surface. The web P is then conducted into a drier section 15 (generally drier drums heated by steam) to set the coating on the web. The web P, substantially dried, is then passed over guide rolls 16 and 17, under guide roll 18 and through a second blade coater comprising a backing roll 19, an applicator roll 20, and a doctor blade 21. Applicator roll 20 rotatively carries coating 22 from the coating pan 23, and applies a second layer of coating, over the first coating layer, to the precoated Web P. Doctor blade 21 (also shown in a trailing position) acts upon the coating to meter a predetermined amount of coating onto the precoated web P and to smooth the surface of the coating. The double coated web on one side is then passed into drier section 24, where the coated web is substantially dried, and then passed around guide rolls 25, 26, 27, 28 and 29, and through a third blade coater comprising a backing roll 30, an applicator roll 31, and a doctor blade 32.

The coating operation for the last two coaters is similar to that of the first two coaters, except that the web P is coated on the side opposite to that previously coated by the first two coaters. This side of the web P, is illustrated in FIGURE 1, is referred to as the felt side of the web. At the third coater, applicator roll 31 rotatively carries coating 33 from the coating pan 34, and applies a first coating layer to the felt side of web P. Doctor blade 32 smooths the coating on web P and wipes excess coating from web P, which is then conducted into drier section 35 to set the first coating layer on the felt side. Web P, which is substantially dried, is then passed around guide rolls 36, 37, 38, 39 and 40, and through a fourth blade coater comprising a backing roll 41, an applicator roll 42, and a doctor blade 43. Applicator roll 42 rotatively carries coating 44 from coating pan 45, and applies a second layer of coating, over the first coating layer, on the felt side of web P. Doctor blade 43 meters and smooths the second coating layer onto the precoated felt side of web P in a similar fashion to blades 14, 21, and 32, as previously shown. At this point the web P has been double coated on each side. Web P continues in travel into drier section 46, where the coated web is substantially dried, over guide roll 47, and into the machine calender stack 48.

The coated web P is finished by the action of calender rolls 49, 50, and 51 forming the stack 48. Rolls 49 and 51 are hard surfaced metal rolls, such as chilled iron. Roll 50 is a resilient, elastic composition roll, and serves to press web P against the metal rolls 49 and 51 as web P passes through the nips defined by the three calender rolls 49, 50, and 51. It is to be understood that calender stack 48 is purely illustrative, and may comprise more or less than the number of calender rolls shown, said rolls being alternating metal and elastic composition rolls, or any combination thereof, as long as two metal rolls are not in contact with each other.

Elastic composition calender roll 50, as shown in FIG- URE 2, is comprised of a metal mandrel 52 having an integrally connected core 53, and an outer solid, cast cover 54 of a plastic or elastic composition which has been placed on the mandrel 52 by a conventional shrink fitting process. It has been found that elastic composition may be employed as the outer cover for a calender roll as a hardness of at least 53 Shore D durometer under operating conditions. The roll must have the ability to substantially maintain its hardness at temperatures up to 200 F., and we prefer that the hardness decreases no more than about 10 durometer units when the temperature rises from room temperature to 200 F., the reason being that as the hardness decreases, the gloss producing ability of the roll also decreases. The roll must also possess suitable resistance to damage. By the term suitable damage resistance, it is understood to mean such resistance that the elastic composition cover will be able to resist and/or recover from the tendency to become permanently indented and marked when several thicknesses of paper pass through the nip between the-elastic composition roll and a metalroll; which mayoccur during threading. operations and. web; breaks,aas previously described. The resistance and: recovery must be at least to the' extent that indentations occurring in, the plastic cover are not injurious to the surface. of the coated web or detrimental to a uniform finishing operation, The elastic composition rolls setjforthin this specification and claims have the properties outlined above.

The elastic composition covers which we have found to be. successful in this invention are, covers of any one of the following polymers: polyamide: polymers, sold under the trade name nylon and defined as nylon 6, polycaprolactam; nylon 6/6, polyhexamethylene adipamide; and nylon; 11, p;oly-w,-aminundecanoic acid; and a polycarbonate. polymer soldunder the trade name Lexan which'may be defined as a polyaryl carbonate manufactured by the General Electric Company and. prepared by reacting phosgene with bisphenol A to give aromatic carbonates of the following general structure:

he if .,l T ta i.

We prefer the use of plastic covers of 1% inches in thickness, but covers of greater or lesser thicknesses may also be employed.

While we have found that an elastic composition roll should possess a hardness value ofatleast 53 Shore D durometer in order to produce a significant increase in gloss, the preferred range of hardness values lies above80 Shore D durometer for most beneficial finishing results. Lexan roll hardness is in the range from about 83 to about 87 Shore D at room temperature. Elastic composition rolls with hardness values up to 94 Shore D durometer have been employed satisfactorily. Rolls possessing even greater hardnesses are not preferred but may be used as long as they do not crushthe web in the manner of conventional chilled iron calender rolls, polishing the high areas .of the web more than the low areas and producing a mottled surface of non-uniform gloss.

EXAMPLE 1 The following table sets forth data showing the effect of the hardness of a resilient roll on gloss development. The paper used for these tests was paper of 32 pounds basis weight (ream of 500 sheets, 25 x 38 inches) double coated on the wire side by two trailing blade coaters, applying a first layer of 4 pounds per ream of a coating composition (53% solids content) comprising mineral pigment and containig 17% starch on clay, and a second layer of 2 pounds per ream ofa coating composition (43% solids content) comprising mineral pigment and containing 17% butadi-ene-styrene latex on clay to produce a coated paper of 38 pounds basic weight. The coated paper was finished by passing it through one nip, formed by one chilled iron roll and one of each of the composition rolls below, loaded at a pressure of about 400 pounds per linear inch of nip. The coated side of the web was against the chilled iron-roll during the finishing operation, and the gloss data is for that side.

Roll Hardness Gloss Rubber 53 21 Rubber 73 28 Rubber 80 29 Nylon (6, 6) 83 30 machine supercalender stack to replace cotton rolls. For.

example, a nylon.roll,of 83 Shore D durometer hardness was used under conditions normally encountered in asuperca-lender t-o finish coatedpaper. Part of the same web of paper was finished by the action of a conventional It can be seen that the nylon roll produces gloss essentially equivalent to that produced by a cotton roll under supercalendering conditions.

Off-machine supercalenders are well known in the art and include conventional features such as a vertical stack of rolls and a frame means, said stack of rolls comprised of a series of alternate hard and soft rolls mounted for rotation and. held in vertical alignment and touching relationship to each other by said frame means; mean for feeding paper to be supercalendered into said stack of rolls andmeans for withdrawing paper after. it has passe-d through said stack of rolls; and drive means for driving at least the lowermost rollof said stack of rolls.

EXAMPLE 2 As showing the nature of the complete process and re sultant product of the present invention, employing double trailing blade coating and elastic composition roll onthe-machine finishing, the following illustration sets forth the preferred method of producing a unique lightweight publication paper having the properties of a smooth printing surface with freedom of mottle and a bulk uncommon to such a lightweight sheet.

A Web of paper of 32 pounds basis weight is double coated on each side by. two. trailing blade coaters, apply ingto each side a base coat of 4 pounds per ream and a top coat of 2 pounds per ream of they same coating formulationsdisclosed. in Example 1. Thepaper is dried to about 6% moisture content throughv the application of heat.

The dried, coated web is then passed through two nips formed by a chilled iron roll, nylon roll, chilled iron roll combination. The Web may be conventionally machine calendered before such finishing treatment, but it is essential that such precalendering be of a very light nature in order to avoid the production of a mottled surface.

As an exaggerated illustration of the web after double coating on one side, reference is made to FIGURE 3'. The baSestock P, which has a relatively rough surface 60 with respect to the smoothness necessary for high quality letterpress printing, has a coating 61 smoothed over its surface 60, and the coating 61 is trowelled into the low areas of basestock P, and forms a relatively smooth top surface 62. A second layer of coating 63 is smoothed over the first layer 61 and the result is a double coated web on one side. with an extremely smooth top surface 64.

In the final finishing on-the-ma-chine with the nylon roll mentioned above, the bottom nip between the nylon roll and the chilled. iron roll is loaded to a pressure of about 400 pounds per linear inch of nip. This finishing action provides for a very uniform finish on the coated surface of the web.

The paper produced by the above method has the following properties:

Gloss 29 Bulk 1.10 Printing smoothness Excellent Mottle Excellent Brightness 75.7 Opacity 88 The relatively low gloss of the final product is attributed to the fact that severe calendering of the web has been avoided. For printing papers, a gloss below 35 is often preferred because of the ease with which the paper can be viewed by a reader after printing of the paper has occurred.

The amount of mottle exhibited by the above paper was negligible, and a mottle rating of excellent was assigned to that paper. Throughout the specification, ratings of poor, good, and excellent have been arbitrarily assigned to papers exhibiting amounts of mottle from extreme galvanized surfaces to surfaces which are free of mottle.

Brightness, opacity, and bulk measurements shown throughout the specification are in accordance with TAPPI Standards T-452m-58, T-425m44, and T- 220m-46, respectively.

Part of the same paper set forth in Example 2 was finished by two nips of three chilled iron rolls loaded at 400 pounds per linear inch at the bottom nip and compared to the finished paper of Example 2.

Gloss 3 5 Bulk 1.01 Printing smoothness Excellent Mottle Poor Brightness 75 .4 Opacity 8 8 Although the chilled iron rolls produce more gloss than in the above preferred method, they provide a mottled surface because of their inability to conform to the web and polish it evenly.

Part of the same paper from Example 2 was also finished by passing the coated web through two nips formed by a cotton roll and two chilled iron rolls in an offmachine supercalender stack. The following data is illustrative for this type operation with a bottom nip loading of 1200 pounds per linear inch.

Gloss 45 Bulk 1.01 Printing smoothness Excellent Mottle Excellent Brightness 74.8 Opacity 86 It can be seen that although the gloss is higher in this finishing operation than in the above preferred operation, the printing smoothness and freedom of mottle in both instances are substantially equivalent. Bulk of the paper finished by the preferred method is higher because the calendering is a less severe calendering operation than is supercalendering. Brightness and opacity are also higher with the preferred finishing method for the same reason. Thus, we have discovered how to produce in one continuous operation a coated paper with the printing quality of a supercalendered sheet, maintaining higher bulk, brightness, and opacity. Such paper finds great utility in the field of publication paper, such as that used in textbooks and magazines. The increased bulk lends to the high degree of opacity obtained, and helps prevent show through when the paper is printed on both sides.

The term printing smoothness as used in the above examples and in the claims may be defined as that smoothness quality exhibited by paper which enables the surface of the paper to make contact with ink on a printing plate when the paper is printed. The test for printing smoothness is carried out under the following standardized conditions. A sheet of paper is printed on a Vandercook No. 4 proof press, using an ink film thickness of 1.71 mg. per sq. in. and a pressure of 143 pounds per linear inch. The ink employed is designated as IPI No. 2 tack graded ink, and the areas printed are 5 inches x 7 inches. The sample in question is evaluated visually by a group of experts using comparison standards and judging the paper on the completeness of coverage of ink on the paper after printing. Paper exhibiting high cover-age is rated as having a high degree of printing smoothness. The evaluation intentionally ignores factors other than smoothness, such as the gloss of the ink or the blackness of the ink, because these properties are influenced by factors other than the smoothness of the paper.

The comparison standards used for evaluation purposes are graded samples previously printed under the above conditions and exhibit varying degrees of printing smoothness. The ink coverage on these samples ranges from a relatively poor coverage assigned an arbitrary value of 60 to a value of 95 for commercial paper finished against a highly polished surface and possessing a mirror image finish, and exhibiting the best ink coverage known in the art. The gradations between 60 and 95 are arbitrarily assigned 5 unit differences, that is, 60, 65, 70, 75, 80, 85, and are gradual differences in ink coverage over the entire scale, but are sufiiciently different between each 5 unit interval that one skilled in the art of evaluating ink coverage can make an obvious distinction between them. Printed paper with values of 90 and 95 is considered as having excellent printing smoothness, values of 80 and 85 are considered good, values of 65 to 75 are considered fair, and values of 60 and below are considered extremely poor for suitable publication paper.

EXAMPLE 3 To show the benefits of the final quality of paper provided by double trailing blade coating, as compared to roll coating followed by trailing blade, the following example is set forth. Pap'er of 32 pounds basis weight was coated on both sides in each instance with 4 pounds per ream of a mineral coating containing 17% starch on clay. The top coat on both sides of the web in each operation was 2 pounds per ream of a mineral coating containing 20% acrylic latex and 80% standard machine coating clay. The coated paper was dried to about 3 moisture content and finished by the preferred method as set forth in Example 2.

In the following chart, DTB denotes the double trailing blade operation and RC+TB denotes that the base coat was applied by a roll coater and the top coat was applied by a trailing blade coater. The BEKK Smoothness values shown are in accordance with TAPPI Standard T- 479sm-48.

WIRE SIDE Coating Calender Gloss BEKK Printing Operation Pressure Smoothness Smoothness 0 17 0 12 90 200 23 Excellent. 200 19 Fair. DTB 400 31 245 Excellent RC+TB 400 24 225 air.

FELT SIDE 0 18 145 0 11 140 200 26 Excellent. 200 19 170 Fair. 400 31 235 Excellent. 400 21 Fair.

It can be seen from the above tables that the gloss and in general BEKK Smoothness of the paper coated by the preferred method were higher evenwithout calendering,

and these properties remained higher when the papers were subsequentiallyl calendered. But: more significantly, it is to be notedthat the printingsmoothness of the paper coated by double trailing blade ranked very. high, even after light calendering and was superior to the paper which was roll coated, followed by trailing blade coating. The property of excellent printing smoothness, at the. relatively low calender pressures, is very. important to the manufacture on the paper machine of a high grade printing paper. The subsequent calendering of the paper by the use of elastic composition rollsin a machine calender, providing a surface which is free of mottle, becomes an important supplement to the overall operations of manufacturing such paper on the paper machine.v Best results are obtained, however, when the coated: web before calendering is as smooth as possible, as by theme of double blade coating.

We have alsofound that best results areobtained when a resin rich top coat, such as- 17% latex on clay, isemployed. Paper of 32pounds basis weight was coated by trailing blade with 4poundsof a coating composition comprising mineral pigment and containing. 17% starch on clay. A two pound per ream top coat containing 17% latex on clay was applied. over the base coat by trailing blade to part of the paper, and a two pound perream top coat of 17% starch on clay was applied over the base coat by trailing blade to the rest' of the paper. The paper was finished by passing it through the nip formed by a nylon roll of 83 Shore D. durometer and. a chilled iron roll.

Calender BEKK Top Coat Pressure, Gloss smoothness Mottle lbs./lin. in.

17% starch on clay..." 200 29 150 Poor. 17% starch on clay"-.. 400 34 185 Do. 17% latex on clay 200 36 165 Good. 17% latex on clay 400 38 200 Do.

It can be seenthat final gloss is increased by employing latex inthe top coat, but, also important to the. manufacture of a high grade printing paper, is the. substantial lack of a mottled surface exhibitedby the latex top coat. Even withnyl-on roll' finishing, a mottled surface was evidenced when a starch-clay top coat wasemployed. Although a butadiene-styrene latex hasbeen set forth in. Example 1, other latices maybe used; We have found that a top coat containing at least about 13% latex on clay should. be used for suitable surface strength.

While. we have disclosed the application of two coats to one side of the web followed by two coats to, the other side of the web to produce double coated paper on each side, we have found that comparable paper can, be produced by first precoating each :side of the web followed by top. coats on each side of the Web without respect to theorder in which the top=coats are applied.

The coating and finishing, processes disclosed. herein may be employed in the manufacture of paper coated only on one side, and it is to. be understood that the coating and finishing. processes may be used on web material. other than paper,:such as paperboard, and.the like.

We. claim:

1-.. The continuous on-the-machine method. of producing high grade printing paper having. a high. degree of printing smoothness and freedom of mottle without supercalendering which comprises applying a first layer of an aqueous coating, composition comprising mineral pigment and adhesive to a traveling webof paper, smoothing the first coating layer and wiping excess coatingfrom. the web, substantially setting the first coating layer, applying a second layer of an aqueous coating composition comprising mineral pigment and adhesive to the surface. of the first coating layer, smoothing said second coating layer over the first coating layer and wiping excess coating from the web, drying the resultant coated web, passing the coated web through a nip formed by a metal roll and aresilient roll to.finish the coated web, the improvement.

['0 CH3 (EHK ln said resilient roll having a Shore D hardness of at least 53 at room temperature.

.2. The continuous on-the-machine method of producing high grade printing paper having a high degree of printing smoothness and freedom ofmottle without supercalendering which comprises applying afirst layer of an aqueous coating composition comprising mineral" pigment and adhesive to a traveling web of paper, pressing a doctor blade in trailing position against thefirst coating layer, smoothing the coating on the web and wiping excess coating from the web with the trailing doctor, blade, thereby trowelling coating into the voids and surface irregularities of the web and leaving a relatively smooth surface, substantially setting the'first coating layer through the application of heat, applying a top coat of a second layer of an aqueous coating composition comprising mineral pigment and adhesive over the first coating layer, pressing a second doctor blade in trailing position against the second coating layer, smoothing the coating over the first coating layer and wiping excess coating from the web with said second, trailing. doctor blade, drying the resultant coated web, passing the coated web. through at least one nip formed by a metal roll and a resilient roll to. finish the coated Web, the. improvement which comprises pressing the coated surface. of' the webv against the metal roll by a resilient roll having a solid, cast: cover of a non-fibrous synthetic polymeric composition selected from the group consisting of polycaprolactam, polyhexamethylene adipamide,poly-w-aminoundecanoic acid, and a. polyaryl carbonate having the structural formula:

0 CH3 L 1113 L said resilient roll having a Shore D hardness in the range of from to 94' at room temperature.

3. The method of claim 2 wherein the web is coated with said first coating layer and said second coating layer on each of its opposite sides before passing through the nip formed by the metal roll and the resilient roll.

4. The method of claim 2 wherein the maximum pressure loading between the metal roll and the resilient roll is about 600-pounds per linear inch.

5. The method of claim 2 wherein the top coat contains at least 13% of a synthetic rubber latex based on the clay content, to provide a substantially mottle free surface to the resultant web..

6. The continuous on-the-machine method of producing high grade printing paper having a high degree of printing smoothness and freedom of mottle, without offmachine supercalendering, which comprises applying a first layer of an aqueous coating composition comprising mineral pigment and adhesive to a first sideof a traveling web of paper, pressing a doctor blade in trailing position against the first coating layer, smoothing said coating on the web and wiping excess coating from the web with the trailing doctor blade, substantially setting the first coating layer, applying over the first coating layer a top coat ofa second layer of an aqueous coating composition comprising mineral pigment and at least about 13% of a synthetic rubber latex based on the clay content, pressing a second doctor blade in trailing position against the second coating layer, smoothing said second coating layer and wiping excess coating from the web with said second trailing doctor blade, drying the resultant double coated web, applying to the second side of the web a first layer of an aqueous coating composition comprising mineral pigment and adhesive, pressing a third doctor blade in trailing position against said first coating layer, smoothing said coating on the web and wiping excess coating from the web with said third trailing doctor blade, substantially setting the first coating layer on said second side of the web, applying a top coat of a second layer of an aqueous coating composition comprising mineral pigment and at least about 13% of a synthetic rubber latex based on the clay content over the first coating layer on said second side of the web, pressing a fourth doctor blade in trailing position against the second coating layer on said second side of the web, smoothing said second layer of coating over the first coating layer and wiping excess coating from the web with said fourth trailing doctor blade, drying the resultant coated web, passing the coated web through at least one nip formed by a metal roll and a resilient roll to finish the coated web, the improvement which comprises pressing one coated surface of the web against the metal roll by a resilient roll having a solid, cast cover of a non-fibrous synthetic polymeric composition selected from the group consisting of polycaprolactam, polyhexamethylene adipamide, poly-w-aminoundecanoic acid, and a polyaryl carbonate having the structural formula:

CH3 l L (3H3 .in

said resilient roll having a Shore D hardness in the range of from 80 to 90 at room temperature.

7. The continuous on-the-machine method of producing high grade printing paper, without off-machine supercalendering, which comprises applying a first layer of an aqueous coating composition comprising mineral pigment and adhesive to a traveling web of paper, pressing a doctor blade in trailing position against the first coating layer, smoothing the coating on the web and wiping excess coating from the web with the trailing doctor blade, substantially setting the first coating layer, applying a top coat of a second layer of an aqueous coating composition comprising mineral pigment and adhesive over the first coating layer, pressing a second doctor blade in trailing position against the second coating layer, smoothing the coating over the first coating layer and wiping excess coating from the web with the second trailing doctor blade, substantially drying the resultant coated web, passing the coated web through at least one nip formed by a metal roll and a resilient roll to finish the coated web, the improvement which comprises pressing the coated surface of the web against the metal roll by a resilient roll; having a solid, cast cover of a polyaryl carbonate which has the structural formula:

its)- if 0l 411, 1

said resilient roll having a Shore D hardness of approximately 83 to 87 at room temperature.

8. The continuous on-the-rnachine method of producing high grade printing paper, without off-machine supercalendering, which comprises applying a first layer of an aqueous coating composition comprising mineral pigment and adhesive to a traveling web of paper, pressing a doctor blade in trailing position against the first coating layer, smoothing the coating on the web and wiping excess coating from the web with the trailing doctor blade, substantially setting the first coating layer, applying a top coat of a second layer of an aqueous coating composition comprising mineral pigment and adhesive over the first coating layer, pressing a second doctor blade in trailing position against the second coating layer, smoothing the coating over the first coating layer and wiping excess coating from the web with the second trailing doctor blade, substantially drying the resultant coated web, passing the coated web through at least one nip formed by a metal roll and a resilient roll to finish the coated web, the improvement which comprises pressing the coated surface of the web against the metal roll by a resilient roll having a solid, cast cover of polycaprolactam, said resilient roll having a Shore D hardness of at least at room temperature.

9. The continuous on-the-machine method of producing high grade printing paper, without off-machine supercalendering, which comprises applying a first layer of an aqueous coating composition comprising mineral pigment and adhesive to a traveling web of paper, pressing a doctor blade in trailing position against the first coating layer, smoothing the coating on the web and wiping excess coating from the web with the trailing doctor blade, substantially setting the first coating layer, applying a top coat of a second layer of an aqueous coating composition comprising mineral pigment and adhesive over the first coating layer, pressing a second doctor blade in trailing position against the second coating layer, smoothing the coating over the first coating layer and wiping excess coating from the web with the second trailing doctor blade, substantially drying the resultant coated web, passing the coated web through at least one nip formed by a metal roll and a resilient roll to finish the coated web, the improvement which comprises pressing the coated surface of the web against the metal roll by a resilient roll having a solid, cast cover of polyhexamethylene adipamide, said resilient roll having a Shore D hardness of at least 80 at room temperature, and pressing the coated surface of the web against the metal roll by the resilient roll to finish the coated web.

10. The continuous on-the-machine method of producing high grade printing paper, without off-machine supercalendering, which comprises applying a first layer of an aqueous coating composition comprising mineral pigment and adhesive to a traveling web of paper, pressing a doctor blade in trailing position against the first coating layer, smoothing the coating on the web and wiping excess coating from the web with the trailing doctor blade, substantially setting the first coating layer, applying a top coat of a second layer of an aqueous coating composition comprising mineral pigment and adhesive over the first coating layer, pressing a second doctor blade in trailing position against the second coating layer, smoothing the coating over the first coating layer and wiping excess coating from the web with the second trailing doctor blade, substantially drying the resultant coated web, passing the coated web through at least one nip formed by a metal roll and a resilient roll to finish the coated web, the improvement which comprises pressing the coated surface of the web against the metal roll by a resilient roll; having a solid, cast cover of poly-w-aminoundecanoic acid, said resilient roll having a Shore D hardness of at least 80 at room temperature, and pressing the coated surface of the web against the metal roll by the resilient roll to finish the coated web.

References Cited by the Examiner UNITED STATES PATENTS 2,344,232 3/1944 Campbell et a1 118123 2,513,394 7/1950 Barrett et a1 1l8249 2,554,663 5/ 1951 Cowgill 117-652 3,043,211 7/ 1962 Appenzeller -170 RICHARD D. NEVIUS, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,222,209 December 7, 1965 Maurice M, Brundige et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 63, after "as" insert long as the roll has column 5, line 51, for "containig read containing line 55, for "basic" read basis column 10, line 2, for "comparises" read comprises column 11, line 34, for "90" read 94 line 55, after "roll" strike out the semicolon; column 12, lines 36 to 38, and lines 61 to 63, strike out and pressing the coated. surface of the web against the metal roll by the resilient roll to finish the coated web", each occurrence.

Signed and sealed this 20th day of September 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. THE CONTINUOUS ON-THE-MACHINE METHOD OF PRODUCING HIGH GRADE PRINTING PAPER HAVING A HIGH DEGREE OF PRINTING SMOOTHNESS AND FREEDOM OF MOTTLE WITHOUT SUPERCALENDERING WHICH COMPRISES APPLYING A FIRST LAYER OF AN AQUEOUS COATING COMPOSITION COMPRISING MINERAL PIGMENT AND ADHESIVE TO A TRAVELING WEB OF PAPER, SMOOTHING THE FIRST COATING LAYER AND WIPING EXCESS COATING FROM THE WEB, SUBSTANTIALLY SETTING THE FIRST COATING LAYER, APPLYING A SECOND LAYER OF AN AQUEOUS COATING COMPOSITION COMPRISING MINERAL PIGMENT AND ADHESIVE TO THE SURFACE OF THE FIRST COATING LAYER, SMOOTHING SAID SECOND COATING LAYER OVER THE FIRST COATING LAYER AND WIPING EXCESS COATING FROM THE WEB, DRYING THE RESULTANT COATED WEB, PASSING THE COATED WEB THROUGH A NIP FORMED BY A METAL ROLL AND A RESILIENT ROLL TO FINISH THE COATED WEB, THE IMPROVEMENT WHICH COMPARISES PRESSING THE COATED SURFACE OF THE WEB AGAINST THE METAL ROLL BY A RESILIENT ROLL HAVING A SOLID, CAST COVER OF A NON-FIBROUS SYNTHETIC POLYMERIC COMPOSITION SELECTED FROM THE GROUP CONSISTING OF POLYCAPROLACTAM, POLYHEXAMETHYLENE ADIPAMIDE, POLY-W-AMINOUNDECANOIC ACID, AND A POLYARYL CARBONATE HAVING THE STRUCTURAL FORMULA: -(COO-(1,4-PHENYLENE)-C(-CH3)2-(1,4-PHENYLENE)-O)NSAID RESILIENT ROLL HAVING A SHORE D HARDNESS OF AT LEAST 53 AT ROOM TEMPERATURE. 